Hi folks, the battery in our ML also laster close to 5yrs. I changed it not because it lost power, but because it started to occationally spill acid. The alternator was ok, so it wasn't an overcharging problem, but the battery is known for braking up this way. I replaced it with an original MB battery, it was expensive but at 4.5+ changing intervals I can afford it, ;-) ...and then I sold it :-(

my 0.02

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'02 C240
'00 LR Discovery
'72 280SE
'67 280SL

---past---

'79 280E sold (RIP)
'86 300E sold
'87 300SDL sold
'90 Laforza sold
'95 320SE sold
'98 ML 320 (sold)